--- a/org/apache/html/dom/HTMLIFrameElementImpl.java	2019-04-17 18:08:03.187783332 +0000
+++ b/org/apache/html/dom/HTMLIFrameElementImpl.java	2019-04-17 18:09:38.640274335 +0000
@@ -17,6 +17,7 @@
 package org.apache.html.dom;
 
 import org.w3c.dom.html.HTMLIFrameElement;
+import org.w3c.dom.Document;
 
 /**
  * @xerces.internal
@@ -161,6 +162,11 @@
         super( owner, name );
     }
 
+    @Override
+    public Document getContentDocument()
+    {
+        return null;
+    }
 
 }
 
--- a/org/apache/html/dom/HTMLFrameElementImpl.java	2019-04-17 19:14:06.833172177 +0000
+++ b/org/apache/html/dom/HTMLFrameElementImpl.java	2019-04-17 19:14:56.755428976 +0000
@@ -17,6 +17,7 @@
 package org.apache.html.dom;
 
 import org.w3c.dom.html.HTMLFrameElement;
+import org.w3c.dom.Document;
 
 /**
  * @xerces.internal
@@ -138,6 +139,11 @@
         super( owner, name );
     }
   
+    @Override
+    public Document getContentDocument()
+    {
+        return null;
+    }
 
 }
 
--- a/org/apache/html/dom/HTMLObjectElementImpl.java	2019-04-17 19:17:26.624199895 +0000
+++ b/org/apache/html/dom/HTMLObjectElementImpl.java	2019-04-17 19:19:23.691802087 +0000
@@ -17,6 +17,7 @@
 package org.apache.html.dom;
 
 import org.w3c.dom.html.HTMLObjectElement;
+import org.w3c.dom.Document;
 
 /**
  * @xerces.internal
@@ -251,6 +252,11 @@
         super( owner, name );
     }
 
+    @Override
+    public Document getContentDocument()
+    {
+        return null;
+    }
 
 }